Natural gas commonly is distributed through a system of pipelines which lead ultimately to residential and other consumers. Various types of valves are used to control the flow of gas to the consumer's meter, one type commonly being referred to as a plug valve.
Plug valves typically have a valve body through which there is a generally cylindrical central bore. The valve body also has an inlet port and an outlet port which extend through the body and communicate through the central bore. Usually, the outer ends of the inlet and outlet ports are threaded so that the valve may be connected to threaded pipe.
Plug valves also have a "plug" or "key" which is mounted so that it can rotate in the central bore of the valve body. The key has a passageway extending through it. When the valve is in an open position, gas can pass through the inlet port, through the passageway in the valve key, and out through the outlet port. When the key is rotated to a closed position, the passageway in the key no longer communicates with the inlet and outlet ports, and the key blocks gas from flowing through the valve.
The valve usually has at least one pair of O-ring seals. There is a upper O-ring located above the ports and passageway and a lower O-ring located below the ports and passageway. These O-rings are situated in grooves which are provided either on the surface of the central bore or on the valve key. The O-rings serve to seal the valve and prevent gas from leaking out of the valve through the small gap which exists between the central bore and the key.
The valve is greased to further reduce the likelihood of leaks. It is important, however, that the grease be distributed through the gap and around the O-rings. One way to help insure that this happens is to provide the valve key with grease channels.
Grease channels typically are cut into the outer surface of the key. The key usually has several of these channels, and they usually run the length of the key between the upper O-ring groove and the lower O-ring groove. Grease may be introduced into the interior of the valve, e.g., through a grease port provided in the valve body. The grease channels then will tend to carry the grease across the surface of the key and central bore and upwardly and downwardly toward the O-rings.
Plug valves of this type have been used widely and with generally good results for many years. They frequently are used as the main shut-off valve for a residence or other structure. After installation of the gas lines to and in the structure, it is common to "blow down" the lines. That is, the main valve is opened, as are all downstream valves, and gas is allowed to blow through the line. This procedure may be performed several times so that all air is removed from the lines, the lines may be checked completely for leaks, and all leaks may be sealed.
During blow down, gas flows through the line at relatively high speed. Workers frequently will not open the valve completely during blow down. When the valve is only partially opened, the grease channels on the key may be rotated into a position where they are over, that is, they communicate with the inlet and outlet ports. When this happens, gas pressure can cause the valve to "cavitate", or to loose grease.
More specifically, grease can be forced upwardly and downwardly in the grease channel over the inlet port and into the O-ring grooves. It then can blow around the circumference of the O-ring grooves until it reaches the grease channel situated over the outlet port. At this point, grease can flow upwardly and downwardly into the grease channel and can be blown out the outlet port. This loss of grease may cause the valve to leak.
An object of this invention, therefore, is to provide a plug type valve which is less susceptible to leaks and which is less likely to cavitate during blow down procedures.
Another object of this invention is to provide such improved plug valves which are as easily and economically manufactured as conventional plug valves.
Those and other objects and advantages of the invention will be apparent to those skilled in the art upon reading the following detailed description and upon reference to the drawings.